1. Field of the Invention
The present invention relates generally to electrical insulators and to electromagnetic energy transmitters and receivers. Particularly, it relates to a process for preparing a structure which is effective as an electrical insulator or as a transmitter-receiver for electromagnetic energy.
2. Description of the Related Art
High performance polymers are being used increasingly by the electronic circuit industry. As cited by Senturia (Proc. of ACS Polym. Matls. Sci. and Eng., Vol. 55, 385,1986), there are four primary applications in the area of microelectronics: (1) as fabrication aids such as photoresists, planarization layers, and ion implant masks; (2) as passivant overcoats and interlevel insulators; (3) as adhesives, and (4) as substrate components. Of utmost importance for the performance of a polymer used for electronic applications is its electrical behavior. To be useful, particularly as a passivant or protective overcoat, the material must be an excellent insulator.
High performance polymers should also find applications on aircraft and spacecraft where structures are needed to efficiently transmit and receive electromagnetic energy, as in radomes, microwave reflectors, waveguides, and the like. Moreover, a need exists in commercial communications for a structure which can be used to efficiently transmit telephonic, radio, and television signals.
U.S. Pat. No. 4,111,906 (Jones et al.) is directed to a novel aromatic diamine and the use of this diamine in the preparation of polymeric materials including polyimides. However, this reference is not concerned with the preparation of a structure which is effective as an electrical insulator or as a transmitter-receiver of electromagnetic energy. Nor is it concerned with the preparation of polymers having low dielectric constants.
U.S. Pat. No. 4,645,824 (Landis et al.)is directed to a solvent polycondensation process for preparing high molecular weight polyimides from dianhydrides and diamines. However, this reference is not concerned with the preparation of a structure which is effective as an electrical insulator or as a transmitter-receiver of electromagnetic energy. Nor is it concerned with the preparation of polymers having low dielectric constants.
Great Britain 1,062,435 is directed to the preparation of polyimides which are useful in the preparation of shaped structures such as films, fibers, filaments, foams, and the like. Like Jones and Landis discussed above, this references does not even mention the dielectric constant of the polyimides, and is not at all concerned with the preparation of structures which are effective as electrical insulators or as transmitter-receivers of electromagnetic energy.
The dielectric constant of commercially available polyimides presently used as state-of-the-art materials for passivants and interlevel dielectrics ranges from approximately 3.2 to 4.0 (depending on frequency and moisture content). The lower limit of 3.2 is obtained on commercial polyimide film DuPont Kapton.RTM. H film only after being fully desiccated. Unfortunately, as the film or coating absorbs moisture, the dielectric constant rises, making measurements and operation of electronic devices complicated.
Accordingly, it is a primary object of the present invention to provide what is not available from the teachings of the prior art, viz., a process for preparing a structure which is effective as an electrical insulator and/or as a transmitter-receiver for electromagnetic energy.
Another object of the present invention is the provision of a process for preparing low dielectric, high temperature, linear aromatic polyimides for use in preparing the above structures.